Rhenium (Re) is a particularly rare metal among rare metals, and is used to reinforce turbine materials for aircrafts, for example.
Rare-earth metal (RE) is used as materials, such as a hydrogen storing metal alloy, rechargeable battery materials, optical glass, a powerful rare-earth permanent magnet, a fluorescent substance, and an abradant, for example.
There is a prior art disclosing that extracting rhenium metal and the rare-earth metal (neodymium, dysprosium) separately at a series of processes from the residue solution as raw material, the residue solution obtained through primary target metal extracted by leaching a mineral resource (for example, Japanese Unexamined Patent Application No. JP-A-2010-285680).
Unfortunately, the process in the prior art, if impurities such as Fe and Al are contained in the residue solution, prevent the rare-earth metals from their proper separate extraction.
The present invention was made in consideration of such a situation, introducing the step of removing the impurities in residue solution, and providing the process for producing rare metal having high robustness to solution composition.